How to link against newlib?

[Christian Haake]

Hi there,
this is my first post so I apologize if my question is a duplicate...
Currently I'm trying to implement the sbrk() system call which is used
by malloc. For this in the syscalls.c file I included a header file
called pagealloc.h.
But while compiling I get a "undefined reference" error because the
associated object file will not be linked.
So my question is how to tell newlib which object file to link with.
Should I customize a Makefile and if yes, which one and how?!?
Thanks in advance for your help.
Chris